This application is related to drive devices for a variety of vehicles, including ride-on mowers, stand-on mowers and walk-behind vehicles such as snow throwers. A hydraulic fluid expansion tank is often associated with these drive devices and is often located external to the housings of these drive devices. It is also known to locate the fluid expansion tank inside a housing of the drive device to prevent damage to the expansion tank, conserve space and eliminate components such as external fluid lines and fittings that are also susceptible to damage. Such internal tanks typically use a siphon system. There is a need for an improved internal expansion tank that will increase flexibility for the drive device manufacturer and allow for reduced hydraulic fluid volume, reduced weight and reduced cost. There is also a need for an internal expansion tank that will provide an improved system for removing entrained air from the hydraulic system.